Astrophotography: Art or Science?

I often receive questions as to how I produce the images that appear on my
site. Most of these are from people who want to learn some of the techniques in
order to improve their own images. Occasionally there is an interest
in how much an image has been modified from the original exposure data, and if
it is truly representative of the actual astronomical object.

In general, astronomical images must all be enhanced to one degree or another
to display all of the information present in them. Indeed, many beginning astrophotographers are very surprised when they start to work with their first
image, for it can appear almost totally black except for the brightest stars in
it. The reason for this is partly because of the limited ability of our current
display devices (computer monitors, printers, etc.) to replicate the range of
brightness levels in the image. The brightness of objects in astronomical images
can vary over a huge range, from the brightest super-giant stars, to the
faintest tendrils of gas in a nebula. There is often interesting detail present
across this whole range, and it is the job of the astrophotographer, in
processing the image, to bring out this data and make it all visible
simultaneously in the final result.

The techniques that are used to bring out this detail are quite powerful, and
so naturally there is an element of care that must be taken not to overdo it. Modern image
enhancement techniques can bring out details that would not otherwise be
visible, but they can also be overused. Sometimes this just results in an
over-emphasis of details that isn't what would be considered a good
representation of the true nature of the object. Other times, "details" can
appear in an image that really aren't there, or at best are misrepresentations
of reality.

By now, there is one point that should be fairly plain: virtually all
astronomical images that are prepared for general viewing have been
significantly modified from their original, scientifically useful form. Because
of this, and because the degree of modification is largely determined by the
judgment and taste of the person doing the processing, we must quickly dispense
with hard-lined notions of what is right and wrong in image processing, for
these also become the province of various individual opinions and personal
preferences. In other words, preparing an image for general viewing is largely
an art. It may be an art that is guided by scientific notions and attention to
detail, but it is still an art.

There may be purist attitudes and ideals which state that any
modification of the image from its original form is somehow "wrong" or
"unethical." About this, there is a key point that can be made. The original,
scientifically useful data in general just aren't that fun to look at. They may
yield answers to enormously important questions, such as the precise distance to
a faraway galaxy or the exact orbit of a near-Earth asteroid, but in general
they lack the aesthetic appeal that has the power to inspire the spirit and the
imagination, to fill us with the desire to know more about what we are
looking at.
Where would the next generation of professional astronomers come from, if it
weren't for these images of celestial sights that conjure up an
interest in the subject in the first place? Indeed, how much public support, and
therefore funding, would a pivotal program such as the Hubble Space Telescope
receive if it were not for the extraordinary images produced by artful
enhancement of some of its scientific data as a side project?

Considerations such as these demonstrate that the art form known as
astrophotography has a very important, if indirect role to play in science.